1. Field of the Invention
This invention relates in general to impact tools and in particular to an improved motorized impact tool using a spring and cam to cause reciprocating impacts.
2. Description of the Prior Art
Cam and spring impact tools normally include a driving shaft rotated by a motor, a hammer mounted for reciprocation, and a cam and roller assembly for translating rotational motion to reciprocation. A spring urges the hammer in one direction to create the impact. The cam is annular with a double inclined camming surface. A pair of cam rollers are rotated, the rise and fall causing the reciprocation of the hammer.
Wear occurs at the drop off shoulders because of the large downward force exerted by the spring at the point of maximum compression. In U.S. Pat. No. 3,302,732, the axle on which the rollers are mounted is free to move a short distance with respect to its rotating shaft in the transverse plane. This allows the rollers to move forward at the drop off shoulder, than rearward after dropping off to create backlash, reducing wear. The movement is provided by means of a barrel shaped axle in one embodiment, and flared ends in the passage for the axle in another.
While successful, it is desirable to provide an impact tool with a backlash feature in which the cam is rotated rather than the rollers. Also it is desirable to mount the axle to the shaft solidly, without a barrel shaped axle and flared passages, which are expensive to manufacture.